Purpose: Identify staff-perceived barriers and facilitators to activity in mechanically ventilated patients in the intensive care unit (ICU). Little is known about WHY inactivity is common in this population. Specific aims were: (1) Describe factors identified by staff that directly influence a decision to implement activity; (2) Correlate patient characteristics such as age, acuity and comorbidities with planned bedrest or out-of-bed activity. Framework: Theory of Planned Behavior (Ajzen,1988). Subjects: 21 registered nurses (RNs) in medical ICU (n=1;12) or surgical ICU (n=9) at an academic medical center provided 28 interviews. Sample characteristics: aged 32 years, female, and 7 years of ICU experience (median 3 years). RNs were caring for patients with hemodynamic stability and 11 days (mean) of mechanical ventilation at the time of the interview. Method: Descriptive, correlational, and cross-sectional. Semi-structured interview. Analyses: RNs planned "no activity/in-bed activity only" among 40% of SICU RNs and 80% of MICU RNs; this resulted in bedrest for 17 patients. The most common reason for bedrest was low respiratory or oxygen reserves in the patient (11/17 patients). Other reasons were risk for compromising tubes or lines and patient weakness (both 9/17). Less common reasons for bedrest were risk for fall (5/17); procedure is planned (2/17) and patient's weight (2/17). RNs planned "out-of-bed activity" for 11 patients; the most common reasons for this level of activity were: stable vital signs (9/11); patient alertness (7/11) and cooperation (7/11); and good respiratory reserve (5/11) or oxygenation (7/11). A less common reason for out-or-bed activity was prescription/order (2/11). Correlations indicated that type of activity (in-bed versus out-or-bed) were not associated with patient age, severity of illness or number of comorbidities. Interpretation: Findings suggest that patient condition rather than resources or prescription/orders drive planned activity. Relevance: Possible misconceptions about barriers to activity such as patient weakness have implications for nursing practice and education.